textproduct: Rapid City

KEY MESSAGES

- A ridge of high pressure will support a strong warming and drying trend through Wednesday, with high temperatures exceeding 80 degrees by Tuesday and approaching 90 degrees in some areas Wednesday.

- A combination of dry fuels, low relative humidities, gusty winds, and the hot temperatures will result in 3 days of widespread near-critical to critical fire weather conditions Monday through Wednesday. New fires could spread rapidly.

- Isolated dry-leaning thunderstorms are possible Wednesday afternoon and evening. At this time, the primary hazards appear to be lightning and wind gusts in excess of 50 MPH.

- An unsettled pattern returns for Thursday through next weekend with much cooler temperatures. The best chance for windy conditions and rain and snow showers will be Thursday.

DISCUSSION

(This Evening Through Sunday) Issued at 217 PM MDT Sun Apr 19 2026

Well...there's quite a bit to talk about as far as the weather is concerned across northeastern Wyoming and western South Dakota this week! On the synoptic scale...we're looking at two diverse regimes. First, a longwave ridge of high pressure that will shift eastward and be our dominant weather enforcer today through Wednesday afternoon, supporting a strong warming/drying trend and critical fire weather conditions. Second, a strong low pressure system that will move in from the west, supporting isolated strong thunderstorms Wednesday late afternoon/evening, the potential for strong winds and widespread rain and snow showers Thursday, and then continued cool and unsettled conditions through at least next weekend. BOTTOM LINE...We're watching Tuesday and Wednesday for hot temperatures, Monday through Wednesday for critical fire weather, Wednesday evening for strong thunderstorms, and Thursday for strong winds and perhaps wetting rain. Let's break down our latest thoughts, trends, and confidence on each potential hazard.

HOT TEMPERATURES: Afternoon high temperatures in the 50s and 60s today (Sunday) will exceed 80 degrees almost everywhere by Tuesday, and will approach 90 degrees across at least our southwestern and central/south-central South Dakota plains by Wednesday. This is 20- 30 degrees above normal/climatology for mid-April. Did not deviate from the deterministic NBM with this afternoon's forecast update, although we do note that the deterministic forecast is running just a couple degrees cooler than the 25th-75th percentile range...which itself is luckily pretty tight. Would expect our high temperature forecast to hold steady or perhaps increase just slightly for each day in future updates, with overall high confidence. At this time, the probability of exceeding 90 degrees is only about 10% Tuesday afternoon, but increases to 20-30% Wednesday afternoon from just east of Rapid City, over to Pierre and Chamberlain, and down to the Nebraska border. Those probabilities haven't changed compared to this time yesterday. While these will be some of the warmest readings we have seen so far this spring, NWS/CDC HeatRisk (which takes many things into account including time of year/climatology, overnight recovery, duration of heat, etc.) remains in YELLOW/MINOR throughout the period, suggesting the heat will primarily only be a concern to those who are extremely sensitive or lack adequate cooling/hydration. Overnight recovery also looks good each night, with low temperatures ranging from the 30s to the 50s. Much cooler high temperatures...a bit below climatology...arrive Thursday and continue through next weekend thanks to longwave troughing and those unsettled conditions.

CRITICAL FIRE WEATHER: With the advancing ridge of high pressure supporting a strong warming/drying trend through Wednesday, a combination of dry fuels, low relative humidities, gusty winds, and hot temperatures will result in a three day stretch of widespread near-critical to critical fire weather conditions Monday through Wednesday. A RED FLAG WARNING has been issued for Monday for portions of northeastern Wyoming and the southwestern and south- central South Dakota plains generally south of Interstate 90, and additional warnings will be possible over this period. New fires could spread rapidly. More details are below in the FIRE WEATHER section. We made minor tweaks to NBM winds/wind gusts Monday afternoon and evening in the forecast, but otherwise NBM RHs and winds looked good for now for each day. Meaningful QPF is NOT expected through Wednesday evening anywhere in our CWA.

STRONG THUNDERSTORMS: Heading toward the arrival of that second weather regime...deterministic models show good agreement in the approaching strong low pressure system reaching southern Idaho by midday Wednesday and somewhere in Wyoming by Wednesday evening, with very good agreement reflected in 500mb height ensemble cluster analysis through this time as well. As it tracks east, it takes on a slight negative-tilt, which from a pattern recognition perspective is often a "red flag" to watch for potential strong to severe thunderstorm activity...especially this time of year with such warm temperatures in place. This potential with this system will largely focus well to the south and east of our region [beyond Wednesday] as reflected in the latest SPC outlooks. However, a perusal of local GFS and NAM model forecast soundings Wednesday evening reveals very dry low-levels with strong "inverted-V" profiles up as high as 600mb, impressively steep low- to mid-level lapse rates over 9 degC/km, DCAPE over 1,300 J/kg (downdraft instability), and even some moderate deep-layer shear over 30kts (largely speed shear), especially from the Black Hills region eastward. Lack of moisture could conceivably be a limiting factor here (and perhaps some cloud cover as reflected in the NBM?), but the GFS in particular models saturation at the top of the boundary layer with decent negative omega (lift), and we do note the GFS, NAM, and NBM guidance are ALL currently simulating shower and convection development. This environment should be favorable for dry-leaning thunderstorms with primary threats of lightning and strong downdraft/outflow winds in excess of 50 MPH. Of course, these threats would also contribute to the fire weather risk as well Wednesday evening. Also of note...various AI, machine learning, and analog guidance from CIPS, NCAR, NSSL, etc. are all modeling anywhere from a 2% to 15% risk of severe weather Wednesday evening, especially across our South Dakota counties. Overall confidence in the exact details is low this far out, but definitely something to watch, both as a general public hazard and for fire partners and any fire crews who may be out in the field by that time.

WIND AND PRECIPITATION THURSDAY: The previously mentioned low pressure system will then track northeast near or over our region Thursday. Some relatively small differences in strength/amplitude and timing/track are noted in both deterministic guidance and 500mb height cluster analysis and EOF patterns by this time. Stuck with WPC QPF in our forecast for now which currently advertises 24-36 hour totals as low as 0.15 inches along the Nebraska border to as high as 0.35 inches from north of Gillette, across our northwestern South Dakota plains, and along our far eastern counties. Yesterday, we noted that 1 500mb height ensemble cluster (about 30% of the ensemble space, GFS-heavy) leaned drier than the mean, but 3 clusters (about 70% of the ensemble space) leaned wetter than the mean with over 0.25 inches of QPF across at least northern portions of our CWA. Today, however, 3 out of 4 ensemble clusters lean drier than the mean with QPF as low as 0.10 inches over the entire region (undercutting our current forecast), while the remaining cluster (currently composed of almost exclusively Canadian and ECMWF members) leans wetter. So yes...uncertainty here. Past experience also warns us that the precipitation forecast tends to trend down more often than up at this range for these types of systems (although while the broader longwave trough is technically split- flow, the southern branch/component targeting our CWA is advertised as fairly robust with a closed low still carried on all long-range models). Bottom line...confidence in just how much QPF we may receive, and chance of wetting rains to take the edge off fire weather concerns, is low, but Thursday is our best shot compared to anything else over the next 7-10 days. We'll need to watch trends in the days ahead. With respect to wind...deterministic NBM guidance continues to come in surprisingly windy from mid-morning to mid- evening Thursday with sustained NW winds possibly over 30 MPH and gusts potentially exceeding 55 MPH almost everywhere. Taking a look aloft...a strong low- to mid-level jet streak is seen rounding the base of the low as it lifts northeast of our area with 700mb flow of 45-55kts. GFS and EC ensemble meteograms for wind gusts at places like Hot Springs, Rapid City, Winner, Buffalo, and Faith are also all starting to show more members gusting over 50 MPH (and even a few outlier members reaching 70 MPH), and the winds are starting to broadly appear on the ECMWF Extreme Forecast Index (EFI) as well. The exact track of the low will impact how the winds play out and we'll see how all guidance continues to trend in the days ahead, but a WIND ADVISORY and/or HIGH WIND WARNING event is certainly plausible.

AND FINALLY: Once the main low lifts northeast of our area Thursday, it still looks to slow down and meander around the northern Plains/southern Canada into next weekend as several other embedded waves/disturbances rotate around it, and with much less model agreement in the details. Broadly speaking, this should spell continued cool temperatures, periods of breezy conditions, and unsettled weather with daily chances of at least some light precipitation. NBM currently carries varying PoPs each day.

AVIATION

(For the 18Z TAFS Through 18Z Monday) Issued At 1127 AM MDT Sun Apr 19 2026

VFR conditions are expected at both TAF sites throughout the forecast period. Winds will diminish through tonight as a high pressure builds over our area.

FIRE WEATHER

Issued At 217 PM MDT Sun Apr 19 2026

Sorry folks...still no good news to share on the fire weather side of things. High pressure building into the region will support a strong warming and drying trend across northeastern Wyoming and western South Dakota today right through Wednesday. Daily afternoon relative humidity values will drop into the 8 to 20 percent range by Monday and stay there each afternoon through Wednesday, while temperatures gradually warm into the 80s to near 90. Forecast confidence is also high in absolutely NO meaningful QPF/rainfall through Wednesday evening. If there is any good news to be had...winds will be much more marginal and somewhat of a limiting factor at times for meeting formal critical fire weather thresholds, but gusts of at least 25 MPH will likely overlap with these dry humidity values in some areas each day, with much stronger winds regionwide Wednesday (south-southwest at 20-30 MPH gusting 30-40 MPH). The combination of dry fuels/ongoing drought, low relative humidities, gusty winds, and hot temperatures will support widespread near-critical to critical fire weather conditions, with multiple RED FLAG WARNINGS possible over this period. New fires may spread rapidly. In collaboration with neighboring NWS offices, the first warning has already been issued for portions of northeastern Wyoming and the southwestern and south-central South Dakota plains for Monday (11 AM to 8 PM MDT). Slam-dunk RH values, marginal winds for this first one. Winds will likely drop off closer to 6 PM, but with continued very dry RHs later into the evening, any new fires that are just getting started will continue to burn pretty effectively, and we don't mind some wiggle room on the tail end of the warning to support ongoing fire partner operations/staffing until the calmest nocturnal winds and moistening start to take hold. Overnight RH recovery each night looks to range from as low as 35% in the Black Hills to as high as 40-70% in plains areas early each morning. Made some tweaks to winds/wind gusts in our forecast Monday afternoon and evening during the current RED FLAG WARNING period, but NBM guidance otherwise looked okay for now through the period.

In addition to the pattern described above...isolated dry-leaning thunderstorms with primary threats of lightning and gusty erratic downdraft/outflow winds in excess of 50 MPH will be possible late Wednesday afternoon and Wednesday evening almost anywhere, another concern to watch for both fire spread and safety of any fire crews who may be in the field at that time (more details on this risk were covered in the above "DISCUSSION" section). On the flip side, Thursday is the day to watch for at least SOME potential for wetting rains, which will also coincide with higher humidity and significantly cooler temperatures (although strong NW winds will be possible regionwide). Our current QPF forecast ranges from as low as 0.15 inches along the Nebraska border to as high as 0.35 inches from north of Gillette, across our northwestern South Dakota plans, and along our far eastern counties Thursday, but confidence at this juncture is very low.

UNR WATCHES/WARNINGS/ADVISORIES

SD...Red Flag Warning from 11 AM MDT /noon CDT/ to 8 PM MDT /9 PM CDT/ Monday for SDZ321-322-325-326-332>335. WY...Red Flag Warning from 11 AM to 8 PM MDT Monday for WYZ315-317.